Electric distribution system employing mercury arc rectifiers



Aug. 7, 1934.

F. P. WHITAKER 1,969,535

ELECTRIC DISTRIBUTION SYSTEM EMPLOYING MERCURY ARC RECTIFIERS Filed Dec..17, 1932 1. A 1 VII INI] Inventor: Frcmk F? Whitaker;

bg Maud His Acco'rneg.

Patented Au "7, 1934 1,969,535.

ELECTRIC DISTRIBUTION s Y s T E M EM- PLOYING MERCURY ARC RECTIFIERSFrank Percy Whitaker, Rugby, England, assignor to General ElectricCompany, a corporation of New York Application December 17, 1932, SerialNo. 647,793 In Great Britain December 23, 1931 3 Claims. (01. 17197)This invention relates to electric distribution true no-load ratio thenthe relay 4 operates to systems employing mercury arc rectifiers andcause the sections of resistance 8 to be gradually more particularly toelectric railways supplied cut out until if the generated load is higherfrom such rectifiers, where the trains are capable than the regeneratedload the resistance will be 5 or regenerative control. entirely out out.The cutting out and in of the 60 It is well known that these rectifierswhile resistance sections 8 may be effected by means capable ofsupplying heavy loads in the forof a motor 9 the circuits of which arecontrolled ward direction cannot receive current from the by the relay4, the motor operating a cam shaft line, so that without some specialarrangement, 10 the cams on which are adapted to close the 10regenerative control is not possible unless other circuits of contactors11 which connect the re- 65 trains are running on the section which cansistances 8 across the direct current bus-bars absorb the current beinggenerated by the train when closed. descending the grade. With such asystem of control, it will be seen The object of this invention is toensure that that the minimum loss in the resistances will 15 trains cangenerate at any time, and under any be incurred throughout a daysworking. It 70 condition of load, and to that end it consists will beseen further that when the differential in automatically coupling aresistance across scheme described above is used, the insertion thedirect current busbars during the time that and cutting out of theresistance sections can be the regenerative load would cause current tomade independent of alternating current voltage actually flow into thesubstation busbars. variations.

This invention therefore consists in the provi- What I claim is: sion ofmeans by which a resistance may be con- 1. In combination, analternating current cirnected to the busbars at the correct time andcuit, an electric railway line and train apparatus for just that periodrequired, during which time thereon capable of regenerative braking,rectithe regenerative loads exceed the generated fier apparatusconnected to the railway line to loads. transmit power thereto from thealternating cur- The accompanying drawing diagrammatically rent circuit,resistance adapted to absorb curillustrates one method of carrying myinvention rent due to said regenerative braking, and means intopractice. As shown in this drawing I prooperating independently ofvoltage variations in -00 vide a rectifier 1 which supplies current toan said alternating current circuit for connecting electric railwayline, the trains thereon being said resistance to the railway line anddisconcapable of regenerative braking. The rectifier necting said,resistance therefrom, said means 1 is supplied with current from thesecondary comprising means for measuring the ratio bewinding 2 of atransformer, the primary winding tween the voltage of the direct currentoutput 35 3 of which is connected to the alternating curcircuit of therectifier apparatus and the voltage rent bus-bars. A differential relay4 has one of the alternating current circuit, and switch coil 5 excitedfrom the mains supplying the means operatively associated with saiddifierenprimary winding of the transformer through a tial relay forcontrolling the connection of said potential transformer 6, the othercoil 7 being resistance to the railway line and the disconnec- 40excited from the direct current bus-bars suption of said resistancetherefrom in response to plied from the rectifier 1. This differentialrelay change in said ratio due to said regenerative therefore measuresthe ratio between the alterbraking. nating current and the directcurrent volts and 2. In combination, an alternating current circan beutilized to detect when the regenerated cuit characterized by a voltagewhich is vari- 5 load tends to be higher than the generated able over asubstantial range, an electric railway load, that is whenever the ratioof direct current line and train apparatus thereon capable of revoltageto the alternating current voltage is. generative braking, rectifierapparatus conhigher that the true no lead ratio. When this nected to therailway line to transmit power occurs the difierential relay is utilizedto insert thereto from the alternating current circuit,

60 gradually resistances 8 in sections across the resistance adapted toabsorb current due to said direct current bus-bars until the ratiobetween regenerative braking, and means operating inthe direct currentand the alternating current dependently of the voltage variation of saidvoltages becomes approximately normal again. alternating current circuitfor connecting said If on the other hand the ratio of direct currentresistance to the railway line and disconnecting 55 to alternatingcurrent voltage is lower than the said resistance therefrom, said meanscomprising a difierential relay for measuring the ratio between thedirect current output voltage of the rectifier apparatus and the voltageof the alternating current circuit, and switch means operativelyassociated with said differential relay for connecting said resistanceto the railway line when said ratio is higher than under no-loadcondition of the rectifier apparatus and to disconnect said resistancefrom the railway line when said ratio is lower than under no-loadrectifier condition.

3. In combination, an alternating current circuit characterized by avoltage which is variable over a substantial range, an electric railwayline and train apparatus thereon capable of regenerative braking,rectifier apparatus connected to the railway line to transmit powerthereto from the alternating current circuit, resistance adapted toabsorb current due to said regenerative braking, a differential relayhaving two windings excited respectively in response to the directcurrent voltage of the rectifier apparatus and to the voltage of thealternating current circuit for measuring the ratio of said twolast-named voltages, and switch control means operatively associatedwith said difierential relay and said resistance, said relay initiatingoperation of said switch control means independently of variation ofsaid alternating current circuit voltage to connect said resistanceprogressively to the railway line when the value of said ratio isgreater then under no-load condition of the rectifier apparatus and todisconnect progressively said resistance from the railway line when saidratio is lower than under no-load condition of the rectifier apparatus.

FRANK PERCY WHITAKER.

